Sulfur-linked bis alkylthio alkylimino-N-alkyl carbamate pesticides of the formula ##STR1## have a wide range of uses in controlling insects and other agronomic pests. Active compounds exhibit a very high level of pesticidal activity and substantially reduced mammalian toxicity and phytotoxicity when compared to other pesticidal compounds having a comparable spectrum of activity against the above mentioned pests.
These compounds are thermally unstable in the presence of a variety of contaminants. Heavy metals and their salts, particularly chloride salts, are especially undesirable. Decomposition is extremely severe in the presence of copper metal, copper chlorides, iron metal, iron chlorides and iron oxide in the form of rust. Other problematic metals include cobalt, nickel and aluminum. Concentrations of as little as 10 ppm are effective if given enough time at temperatures of 60.degree. C. or higher. Sulfur and sulfide salts can also induce decomposition, although usually at rates slower than those of chloride-containing systems. Some organic decomposition initiators have also been identified, including pyridine, pyridine hydrochloride, di- and trisulfides, amines, peroxides and acids (e.g. acetic and citric acids). Presence of 5% or more methomyl or its oxime can also induce decomposition.
The principal object of this invention to provide a method to inhibit or retard the thermal decomposition processes that may occur in bulk quantities of sulfur-linked bis alkylthio-alkylamino-N-alkyl pesticides when they are dried at elevated temperatures or stored for extended periods of time, especially in warmer climates. It is a further object to provide stable wettable powders and dispersible granular formulations of these pesticides.